Space-charge wave detector tubes



Aug. 27, 1957 H. HUBER 2,804,569

SPACE-CHARGE WAVE DETECTOR TUBES Filed Dec. 31, 1953 2 Sheets-Sheet l Aug. 27, 1957 H. HUBER l 2,804,569

SPACE-CHARGE WAVE DETECTOR TUBES Filed Dec. 31, 1955 2 Sheets-Sheet 2 *i E SvomY .5. p2 wfg/vra? e5 F/G gm 4% f5.

er A

United States Patent Ofiline 2,804,569 Patented Aug. 27, 1957 SPACE-CHARGE WAVE DETECTOR TUBES Harry Huber, Paris, France, assigner to Compagnie Generale de Telegraphie Sans Fil, a corporation of France Application December 31, 1953, Serial No. 401,661

Claims. (Cl. S15-3.5)

In a copending application Serial Number 144,502 filed on February 16, 1950 for Ultrahigh-Frequency Amplifier Tube there is described a tube comprising an interaction space limited by two smooth parallel electrodes. In this space are propagated in a direction parallel to the surface of the two electrodes one or several electron beams. These beams are subjected to the action of a constant magnetic field and of a constant electric field, the respective lines of force thereof being perpendicular to the mean direction of propagation of the electron beam and to each other. The electric field is created by applying to the two above electrodes xed and different potentials.

It is known that, if at the input end of the interaction space there is fed an electromagnetic wave of ultra-high frequency, this wave produces in this 'or these beams an alternating current having the same period as the wave and which is progressively amplified from the input end to the output end of the interaction space.

The electron beam behaves as a fluid which is owing through a passageway and is disturbed at a point, this disturbance resulting in a slowing down of the current streams situated near one of the edges of the passageway and an accelerating of the streams situated near the other edge. Thus there is created a speed gradient in the direction perpendicular to that of the fluid flow, the mean speed of the current remaining constant. This disturbance is propagated and amplied along the current at the mean Velocity of the latter and gives rise to waves having an amplitude that increases with the distance from the source of the disturbance. These waves are of the same nature as that which is the cause of the disturbance.

The tube described in the aforementioned patent application comprises an input circuit for feeding the ultrahigh frequency wave to the tube, this circuit being situated near the emitting system, an interaction space and an output circuit enabling the amplified wave to be picked off.

The present invention has for its object a U. H. F. tube which may more particularly be used as a detector and which also comprises an interaction space which is limited by two smooth electrodes. According to the invention the tube comprises means for making the electric field existing in the interaction space limited by two electrodes having smooth surfaces, independent of electric fields existing respectively in the input circuit and in the output circuit. It is thereby possible to vary the electric field prevailing in this interaction space while keeping unaltered the electric fields existing in the input and output circuits. The magnetic field remains always constant throughout the whole tube.

According to a preferred embodiment, the tube according to the invention, which will be termed hereinafter a Diocotron tube, comprises the following elements:

(a) An evacuated envelope;

(b) Means for creating inside this envelope a constant magnetic field;

(c) An input circuit comprising: means for feeding to the tube an electromagnetic ultra-high frequency wave;

1?; a cathode for producing an electron beam and an electronic `optical system of the type which is conventionally used in travelling wave tubes operating with a magnetic eld, for example that described in the copending application Serial Number 290,530 of May 28, 1952, now Patent No. 2,774,913 (inventor D. Charles).

(d) A first interaction space limited by two electrodes parallel to each other and to the focussed electron beam, one of these electrodes being a delay line;

(e) An amplifying circuit, `or Diocotron space, defined by two smooth electrodes having smooth surfaces, the potential of one of these electrodes being high relative to that of the cathode;

A source of D. C. current for applying to these electrodes different xed potentials, the positive electrodes (for instance 1000 v.) having a high positive potential relative to the cathode, the magnetic field being perpendicular both to the direction of propaga-tion of the beam and to the electric field thereby created. The negative electrodes have a slight negative potential with respect to the cathode;

(g) A resistor series inserted in the supply circuit yof one of the two smooth electrodes, preferably of the electrode whose potential is positive, and means for collecting across said resistor the detected voltage;

(h) At the end of the tube remote from the cathode a collector electrode having high positive potential;

At least one of the two said electrodes having smooth surfaces is electrically isolated from the other electrodes.

The invention will be better understood from the following description with reference to the accompanying drawings wherein:

Fig. l shows diagrammatically in longitudinal section a tube according to the invention;

Fig. 2 shows `a transverse section along the line 2-2 of Figure l;

Figs. 3 and 4 are curves which explain the operation of the tube according to the invention;

Fig. 5 shows the tube of Fig. l used as a mixer;

Fig. 6 shows a modification of the part CD of the connections of the tube of Fig. l.

The tube according to the embodiment shown in Fig. l comprises inside an evacuated envelope 1:

(a) An input circuit A which comprises a cathode 2, the potential of which is taken as the origin of the potentials, for emitting a beam 3; an electronic 'optical system 10 for directing the beam 3 in the axial direction, this system being for example of the type described in the aforementioned copending application in the name of D. Charles and comprising in particular an electrode 4 and an electrode 5; an electrode 6 prolonging the electrode 5, in electric contact with the latter (these ltwo electrodes generally form an integral body), comprising a portion 7 parallel to a delay line 8 and having a potential -Vs, in order to keep the electrode 6 at a potential which is slightly negative with respect to the cathode, this step being necessary as is known for suitable focussing of the beam 3.

Two lmagnets 9 (Fig. 2) create throughout the whole of the tube 1 a field H perpendicular to the plane of Fig. l. The assembly formed by the electronic optical system 10 and the magnet 9 fo-cusses the electrons into a beam 3 the mean direction of which is parallel to the surfaces of the electrodes between which it is propagated.

(b) An amplifier circuit B which comprises two electrodes 11 and 12 which are flat, smooth and parallel and are respectively in the prolongation of the electrodes 7 and 8 but are electrically insulated from the latter. One of the electrodes 12, which is in the prolongation `of the electrode 7, is connected to an adjustable negative potential source and the electrode 11 is connected to 'an adjustable positive potential source. These two electrodes limit the interaction or Diocotron space.

As already stated the magnetic field H is perpendicular to the beam 3 and to the electric fields existing respectively between the electrodes 7 8 and 11-12.

Voltages Vop and Vus are respectively provided by two variable voltage sources P1 and P2. A resistor Rp is series connected between the source P1 and the positive pole of `a high potential source V0, for instance 1000 v., which is also applied to the electrode 17.

A signal fed through the line 15 to the delay line 3 modulates in thickness the electron beam. The depth of modulation is a direct function of the signal intensity. This modulation propagates along the beam with the velocity of the latter.

The signal having a given intensity will therefore cause a number of electrons to impinge on the positive electrode 11. The shorter the distance from the beam to the electrode 11 in the absence of any signal, the greater the number of electrons reaching the electrode 11.

For a given value of this distance, the number of electrons collected by the electrode 11, when 'a signal is fed to the tube, is a direct function of the signal intensity.

Therefore, the tube operates as a detector since the variations of the signal intensity are impressed on the current flowing through the electrode 11.

It has been stated above that this current essentially depends on the position of the electrode beam with respect to the electrode 11 in the absence of any signal. lt may be shown, and this has been done in a copending application for Improvements in Space Charge Wave Tubes filed on the same day as the present application, that this position maybe adjusted by varying the voltages.

Fig. 3 shows how the current owing through the electrode 11, varies as a function of the input signal amplitude. The current curves shown have been obtained for various values of Vop, Vos being adjusted once for all. It will be seen that current is directly proportional to the amplitude of the input signal Pe.

The detection takes place across the terminals of a resistor Rp. For various values of Vop the detection characteristic shown in Fig. 4 are obtained.

Curve m is obtained when, in the absence of any signal, the current fiowing in the electrode 11 is zero. In the case of curve n there is no current flowing in the absence of any signal and such current appears when a signal is fed to the tube. in thc case of curve o, the beam is still farther from the electrode 11, when there is no signal. This -current flows only when the level of the signal is higher than a predetermined one.

Applicant has Vobtained a detection characteristic having a sensivity of 0.002 A for law with an experimental tube. This value could certainly be improved by increasing the gain of the tube.

The detection sensivity may also be increased by utilizing a detection resistance of high resistivity.

In principle electrode 12, could also be used as detecting electrode, since it may be given a positive potential with respect to the cathode, whereby the beam is brought nearer to this electrode. Fig. 6 shows the modifications which may be applied to the portion CD of the connections of Fig. l. A resistor Rs is series connected between the source Pz and the point D. The detection takes place across the terminals of the resistor Rs. However, in such an event, this electrode may give rise to a secondary emission, the reason being that its potential would be low with respect to the potential of the electrode 11. Such an emission could be disturbing since the detector current could be decreased in this wave or even reversed.

The detector thus provided displays many advantages namely great sensivity and great efficiency, good linearity, large band-pass and strength.

The tube shown in Fig. 5, which is similar to that shown in Fig. 1 may be used as a frequency mixer. Two waves having respectively frequencies F1 and F2 are fed to the line 15 through different transmission lines, for instance wave guides 151 and 152.

Resistor D is inserted in the circuit of the electrode 11 and a voltage having a frequency F1, F2 may be collected across the terminals of the resistor D.

In order for the U. H. F. fields provided respectively by the two F1 and F2 frequency waves to interact with the electron beam, a delay line 8 may be used, causing F1 and F2, high frequency elds to propagate with substantially the same phase velocity along said delay line.

The two waves considered are then fed together to the electron beam and amplified together in the Diocotron" space of the tube. The beam is adjusted by adjusting the voltages respectivelyjapplied to the electrodes 11 and 12, as shown in the case of the detector. A wave having a frequency Fi-Fz may be abstracted across the terminals of the resistor D.

What I claim is:

l. Ultra high frequency electronic discharge tube, of the type having within an evacuated envelope, a cathode land an electron optical system for emitting and focusing an electron beam and a collector for collecting the electrons of said beam and means for providing within said envelope an electric and a magnetic field perpendicular to each other and to the direction iof the beam comprising: an input for ultra high Ifrequency energy, and a first electrode in the form of a delay line connected to said input, a second electrode having a smooth surface, said first and second electrode being substantially in prolongation of and electrically insulated from each other said second electrode with a smooth surface being located between said first electrode and said collector, energized connections for bringing to high electric positive lpotentials said first and said second electrodes with respect to said cathode, a third electrode, a fourth electrode having a smooth surface, said third and fourth electrodes being in prolongation of each other, said first and third, second and fourth electrodes being located respectively in front and Vspaced from each other, for limiting respectively a first and a second interaction space, said cathode being located for propagating said electron beam within said interaction spaces in the above order, and energized connections to `said third and said fourth electrodes for bringing them respectively to potentials negative with respect to the potential of said cathode.

2. In combination: tube according to claim 1 and voltage regulating means -for controlling the electric field in -said interaction space limited by said second and fourth electrode.

3. In combination: a tube according to claim 1 and a resistor series connected between said second electrode and said energized connection thereof.

4. `In combination: a tube according to claim l and a resistor series connected between said fourth electrode and said energized connection thereof.

5. `In combination: a tube Iaccording to claim 1 means to feed together to Vsaid first electrode in the form of a delay line two waves having different frequencies, and a resistor series connected with one of the above electrodes having a smooth surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,137 Hnsen July 1, 1952 2,607,904 Lerbs Aug. 19, 1952 

